Vasomotor symptoms (VMS), referred to as hot flushes and night sweats, are the most common symptoms associated with menopause, occurring in 60% to 80% of all women following natural or surgically-induced menopause. VMS are likely an adaptive response of the central nervous system (CNS) to declining sex steroids. To date, the most effective therapies for VMS are hormone-based treatments, including estrogens and/or some progestins. Hormonal treatments are very effective at alleviating VMS, but they are not appropriate for all women.
VMS are caused by fluctuations of sex steroid levels and can be disruptive and disabling in both males and females. A hot flush can last up to thirty minutes and vary in their frequency from several times a week to multiple occurrences per day. The patient experiences a hot flush as a sudden feeling of heat that spreads quickly from the face to the chest and back and then over the rest of the body. It is usually accompanied by outbreaks of profuse sweating, and may sometimes occur several times an hour, and it often occurs at night. Hot flushes and outbreaks of sweats occurring during the night can cause sleep deprivation. Psychological and emotional symptoms are also observed, such as nervousness, fatigue, irritability, insomnia, depression, memory loss, headache, anxiety, nervousness or inability to concentrate, and are caused by the sleep deprivation following hot flush and night sweats (Kramer et al., In: Murphy et al., 3rd Int'l Symposium on Recent Advances in Urological Cancer Diagnosis and Treatment-Proceedings, Paris, France: SCI: 3-7 (1992)).
Hot flushes may be even more severe in women treated for breast cancer for several reasons. Many survivors of breast cancer are given tamoxifen, the most prevalent side effect of which is hot flush, and many women treated for breast cancer undergo premature menopause from chemotherapy. Women with a history of breast cancer are also generally been denied estrogen therapy because of concerns about potential recurrence of breast cancer (Loprinzi, et al., Lancet, 2000, 356(9247): 2059-2063).
Men also experience hot flushes following steroid hormone (androgen) withdrawal. This is true in cases of age-associated androgen decline (Katovich, et al., Proceedings of the Society for Experimental Biology & Medicine, 1990, 193(2): 129-35) as well as in extreme cases of hormone deprivation associated with treatments for prostate cancer (Berendsen, et al., European Journal of Pharmacology, 2001, 419(1): 47-54. As many as one-third of these patients will experience persistent and frequent symptoms severe enough to cause significant discomfort and inconvenience.
The precise mechanism of these vasomotor symptoms is unknown but generally is thought to represent disturbances to normal homeostatic mechanisms controlling thermoregulation and vasomotor activity (Kronenberg et al., “Thermoregulatory Physiology of Menopausal Hot Flashes: A Review,” Can. J. Physiol. Pharmacol., 1987, 65:1312-1324).
The fact that estrogen treatment (e.g. estrogen replacement therapy) relieves the symptoms establishes the link between these symptoms and an estrogen deficiency. For example, the menopausal stage of life is associated with a wide range of other acute symptoms as described above and these symptoms are generally estrogen responsive.
It has been suggested that estrogens may stimulate the activity of both the norepinephrine (NE) and/or serotonin (5-HT) systems (J. Pharmacology & Experimental Therapeutics, 1986, 236(3) 646-652). It is hypothesized that estrogens modulate NE and 5-HT levels providing homeostasis in the thermoregulatory center of the hypothalamus. The descending pathways from the hypothalamus via brainstem/spinal cord and the adrenals to the skin are involved in maintaining normal skin temperature. The action of NE and 5-HT reuptake inhibitors is known to impinge on both the CNS and peripheral nervous system (PNS). The pathophysiology of VMS is mediated by both central and peripheral mechanisms and, therefore, the interplay between the CNS and PNS may account for the efficacy of dual acting SRI/NRIs in the treatment of thermoregulatory dysfunction. In fact, the physiological aspects and the CNS/PNS involvement in VMS may account for the lower doses proposed to treat VMS (Loprinzi, et al., Lancet, 2000, 356:2059-2063; Stearns et al., JAMA, 2003, 289:2827-2834) compared to doses used to treat the behavioral aspects of depression. The interplay of the CNS/PNS in the pathophysiology of VMS and the presented data within Loprinzi, et al., were used to support the claims that the norepinephrine system could be targeted to treat VMS.
Although VMS are most commonly treated by hormone therapy, some patients cannot tolerate estrogen treatment (Berendsen, Maturitas, 2000, 36(3): 155-164, Fink et al., Nature, 1996, 383(6598): 306). In addition, hormone replacement therapy is usually not recommended for women or men with or at risk for hormonally sensitive cancers (e.g. breast or prostate cancer). Thus, non-hormonal therapies (e.g. fluoxetine, paroxetine [SRIs] and clonidine) are being evaluated clinically. WO9944601 discloses a method for decreasing hot flushes in a human female by administering fluoxetine. Other options have been studied for the treatment of hot flushes, including steroids, alpha-adrenergic agonists, and beta-blockers, with varying degree of success (Waldinger et al., Maturitas, 2000, 36(3): 165-168).
α2-Adrenergic receptors play a role in thermoregulatory dysfunctions (Freedman et al., Fertility & Sterility, 2000, 74(1): 20-3). These receptors are located both pre- and post-synaptically and mediate an inhibitory role in the central and peripheral nervous system. There are four distinct subtypes of the α2-adrenergic receptors, α2A, α2B, α2C and α2D (Mackinnon et al., TIPS, 1994, 15: 119; French, Pharmacol. Ther., 1995, 68: 175). A non-select α2-adrenoceptor antagonist, yohimbine, induces a flush and an α2-adrenergic receptor agonist, clonidine, alleviates the yohimbine effect (Katovich, et al., Proceedings of the Society for Experimental Biology & Medicine, 1990, 193(2): 129-35, Freedman et al., Fertility & Sterility, 2000, 74(1): 20-3). Clonidine has been used to treat hot flush. However, using such treatment is associated with a number of undesired side effects caused by high doses necessary to abate hot flush described herein and known in the related arts.
Chronic pain comes in many forms, including visceral, inflammatory or neuropathic and crosses all therapeutic areas. It is a debilitating condition that exerts a high social cost in terms of productivity, economic impact and quality of life and current therapies have limited efficacy. Currently, first-line pharmacological treatments for neuropathic pain (i.e., diabetic neuropathy and post-herpetic neuralgia) and fibromyalgia include off-label use of the tricyclic (TCA) antidepressants (e.g., amytriptyline) and anticonvulsants (e.g., gabapentin) (Collins et al., J. Pain Symptom Manage. 2000, 20(6):449-58; and Marcus Expert Opin Pharmacother. 2003, 4(10): 1687-95). However, these therapies are only effective in 30-50% of patients and produce only a partial reduction in pain (˜50%). In addition, the clinical benefits of these therapies are often outweighed by the side effects, including dry mouth and sedation. Therefore, newer classes of compounds including non-TCA antidepressants are being evaluated preclinically and clinically for chronic pain indications, and recently duloxetine was approved for the treatment of diabetic neuropathy. Although more tolerable than the older tricyclic antidepressants, these newer compounds are not devoid of side effects that include sexual dysfunction, weight gain and nausea.
While the precise pathophysiological mechanisms involved in the development and maintenance of chronic pain states are not fully understood, the pathways involved in pain perception and modulation have been well described and characterized (Gebhart, In: Yaksh T L, editor. Spinal afferent processing, New York: Plenum, 1986. pp 391-416; Fields, et al., Annual Review of Neuroscience 1991, 14: 219-245; Fields, et al. In: Wall P D, Melzack R, editors. Textbook of pain, London: Churchill Livingstone, 1999, pp 309-329; Millan, et al. Progress in Neurobiology; 2002, 66:355-474). A major component of this descending pain inhibitory system involves the noradrenergic pathway (Zhuo, et al., Brain Research 1991; 550:35-48; Holden, et al. Neuroscience 1999; 91: 979-990). It is assumed that norepinephrine (NE), and to a lesser extent serotonin (5-HT) reuptake inhibitor NRIs and SRIs, attenuate pain by preventing presynaptic reuptake of NE/5-HT leading to increased postsynaptic NE/5-HT levels and sustained activation of this descending pain inhibitory pathway. A meta-analysis of antidepressants and neuropathic pain comparing the efficacy of known NRIs, mixed NRI/SRIs and SRIs determined that compounds with NRI activity were more effective in reducing pain, and that select SRIs did not significantly differ from placebo (Collins et al., J. Pain Symptom Manage. 2000, 20(6): 449-58). This analysis suggests that compounds with greater NRI versus SRI activity will be more effective for the treatment of pain.
Given the complex multifaceted nature of pain and of thermoregulation and the interplay between the CNS and PNS in maintaining thermoregulatory the homeostasis, multiple therapies and approaches can be developed to target the treatment of pain and vasomotor symptoms. The present invention provides novel compounds and compositions containing these compounds directed to these and other important uses.